It is well-known in the screen printing processes to print through screens of metal or fabric, where the mesh is created by perpendicular filaments. Such screens may be made from a number of materials including, but not limited to, phosphor bronze, copper, molybdenum, gold, platinum or stainless steel. Also, and more commonly, screens are made of synthetic material such as nylon and Dacron. Mesh sizes of 80 to 400 (wires and/or filaments per inch) may be used.
Typically, to form the printing stencil from such screens, the entire screen is filled with a filler, such as gelatin. After filling, excess filler is removed from the printing areas, without removing filler intended to plug the non-printing mesh areas in the screen.
U.S. Pat. No. 3,696,742 to L. P. Parts et al. discloses what is described as an improved screen-printing stencil in which the non-printing areas of a conventional screen are closed with a solid polymer capable of undergoing residue-free depolymerization. After all the apertures in the screen are filled, the prospective printing areas are irradiated with a laser beam of sufficient intensity to depolymerize the polymer from these printing areas and completely evaporate the depolymerization products. The evaporation of the depolymerization products leaves selected areas of the screen mesh open for the passage of ink. In at least some applications the laser beam can be shaped by using a stencil into which the desired pattern or patterns have been cut. Alternately, irradiation can be through a mask laid upon the filled screen.
Japanese application No. 60-230338 to Sanyo also discloses the use of a laser beam to cut a design in a stencil or template material, which stencil is then adhered to a mesh screen, to eliminate the need for photosensitive emulsions. The screen is used for printing thick film integrated circuits.
European Patent No. 0,266,622 to R. Bellot discloses a cylindrical form for screen printing, comprising a cylindrical sieve around which a template is secured. The template can be of plastic and can be secured to the sieve by heat shrinking, heat treatment for adhesive. To determine the printing pattern a laser is used to selectively remove portions of the template.
West German patent application DT 25 39 845 to A. Beckert discloses a printing process which uses a cylindrical perforated carrier screen, with a 40 to 60 line screen distributed homogeneously. The holes in the cylindrical carrier screen can be produced by a laser beam. The screen is then covered with a photo-lacquer layer, or copper, or plastics. Cut outs are formed in this layer having the shape of the letter, etc., to be printed.
Finally, PCT WO 86/04549 to S. Ruckl discloses a screen printing stencil made by perforating a foil uniformly and then coating it so that all the perforations are filled. The foil is then wrapped on a cylinder and a laser beam is then directed on the foil to bare selected perforations in the desired pattern.
All of the above described apparatus and methods require the use of a screen or equivalent (the sieve of Bellot; the perforated cylinder of Beckert; the perforated foil of Ruckl) in which the perforations or openings are filled and then certain perforations/openings selectively opened by a laser beam (Parts and Ruckl) or non-wanted perforations/openings are covered with a stencil (Beckert, Bellot and Sanyo).
U.S. Pat. No. 4,497,848 to A. S. Baran discloses a method and apparatus for producing a machine readable marking, such as a bar code marking, on work pieces. The method includes producing a stencil of the marking in stencil material (such as paper, plastic or metal) by incising the stencil material or by controllably burning the stencil material with a focused laser beam. Coating material is then applied through the stencil.
Although, as is obvious from the above references, there has been a long felt need in the art for a precise "screen" for use in printing, it was not until the subject invention that an inexpensive, accurate method of producing such a screen was feasible.
The subject apparatus and method have a number of advantages over the prior art. The single step of punching or ablating the desired hole pattern(s) in the template stock material with a laser is faster than prior art processes. It avoids the expense and time consuming steps of forming a screen, filling the screen and then removing selected portions of the fill to re-expose portions of the screen. The invention also allows for varying both the pitch of the holes and the size of the holes in a single screen which is not possible with prior art screens. The process also avoids waste removal associated with the prior art. Finally, the apparatus and method of forming the screen facilitates automation of the entire process, from forming the screen to printing and drying. The inking station is automatic, repeatable, and prints on both strokes (forward and backward). As such, the subject invention provides a solution to a long existing problem.